Study Of Stress Effect On Shear Strength Of Single Saw-tooth Structural Plane

The rock mass is a discontinuity which is cut by structural planes with different shapes and mechanical properties.The failure of rock mass is mainly due to structural plane and shear failure is the main form of structural plane.Most scholars think that shear strength of structural plane is related to the size,but the study of stress effect is still insufficient.In this paper,based on the laboratory test and numerical simulation,the shear characteristics of structural plane under normal stress were studied by direct shear apparatus,and the stress effect law of shear strength of the structural plane was analyzed.According to the analysis,the following work has been done.Firstly,the direct shear apparatus for structural plane was invented,which can be used for testing stress effect.The experimental results of direct shear apparatus are consistent with the existing data,so direct shear apparatus is reliable.Secondly,through the uniaxial compression test of four kinds of mix proportion specimens,the normal stress value of direct shear test was determined.New design moulds were made considering the fluctuation angle,saw-tooth height,process,assembly and so on.Thirdly,shear characteristics of straight and single saw-tooth structural plane under normal stress were studied.The results shows that there is no stress effect on shear strength of straight plane;shear strength of single saw-tooth structural plane has obvious stress effect;with the increasing of normal stress,peak shear strength increases firstly and then tends to be stable.Fourthly,the influence factors of shear strength were analyzed considering roughness of structural plane,normal stress,joint wall compressive strength and friction angle.The results shows that there is no stress effect on peak friction angle of straight plane;peak friction angle of single saw-tooth structural plane has obvious stress effect;with the increasing of normal stress,peak friction angle decreases firstly and then tends to be stable.Fifthly,peak shear strength of single saw-tooth structural plane is related to inclination angle,saw-tooth height and saw-tooth area.Other factors unchanged,with the increasing of saw-tooth height,shear strength shows an approximately linear increase and relationship between shear strength and saw-tooth area also shows the same regularity.Finally,the numerical simulation of single saw-tooth structure plane is carried out by PFC.Comparisons are made between laboratory tests and numerical simulation.In general,satisfactory agreement is found.